Sphingosine1-phosphate (S1P) is a pleiotropic autocrine and paracrine signaling small lipid molecule that directs a wide range of biological responses through a family of high-affinity G protein-coupled receptors (S1P1-S1P5). The proposed studies will interrogate the cooperative functions of S1P1 and S1P3 subtype activation in the microvasculature to promote inflammation resolution and bone repair. Although monocyte recruitment is a critical component of the normal bone healing cascade, persistent monocyte accumulation can progress into chronic inflammation and impede recruitment and differentiation of osteoblastic progenitor cells required for tissue regeneration. Preliminary studies show that S1P1 antagonizes pathologic inflammation by preventing monocyte adhesion to activated endothelium, and that sustained delivery of receptor selective drugs targeting S1P1 and S1P3 subtypes from 3-D biodegradable polymers promotes microvascular network maturation and increases osseous tissue ingrowth in critical sized cranial bone defects. Thus, the overarching hypothesis of this proposal is that sustained delivery of pharmacological agonists targeting S1P1 and S1P3 from biodegradable polymers promotes osseous defect healing by locally suppressing monocyte accumulation to tissue implants and promoting recruitment of mesenchymal progenitor cells (MPCs) to regenerate bone. AIM 1 will test the hypothesis that S1P1 and S1P3 act synergistically to promote mesenchymal stem cell adhesion to endothelium. AIM 2 tests the hypothesis that selective stimulation of S1P1/S1P3 from synthetic degradable polymers prevents local accumulation of monocytes and promotes homing of mesenchymal progenitor cells in a cutaneous model of chronic inflammation. AIM 3 tests the hypothesis that S1P1 and S1P3 modulation of inflammatory and mesenchymal progenitor cell recruitment will enhance bone healing outcomes. PUBLIC HEALTH RELEVANCE: The replacement or restoration of function to traumatized, damaged, or lost organs and tissues is an increasingly significant clinical problem. It is estimated that only 24,422 received organ transplants of a possible 79,512 patients on the transplantation wait list in 2002. In addition, it is currently estimated that over 1.5 million skeletal injuries alone will require tissue graft reconstruction in the US each year, and these numbers will continue to grow as the life expectancy of the population increases. Thus, the development of effective strategies to harness inflammation for revascularization and regeneration of osseous tissue defects is a significant medical need.